Effects of optical isomers of clenbuterol on the relaxant response in rat uterus

Previous works have shown that the administration of the racemic beta -adre noceptor agent clenbuterol produces a desensitization of the relaxant respo nse in rat uterus. The aim of this work was to study the effects of the opt ical isomers of clenbuterol on the relaxant response in rat uterus. The adm inistration of (L)-clenbuterol (0.25 mg per kg per dap) over 1 or 10 consec utive days, produced a reduction of the relaxant response to isoproterenol in uterine rings precontracted with 50 mM KCI from oestrogenic rats. The ad ministration of (D)-clenbuterol (0.25 mg per kg per day) over 1 or 10 days did not affect the relaxant response of isoproterenol. (L)-clenbuterol also produced a concentration-dependent relaxant effect that was not observed w ith (D)-clenbuterol. These results show that the beta -adrenergic relaxant response and the desensitization of the relaxant effect to isoproterenol is due to the (L)-isomer and that the (D)-isomer is not involved in these eff ects. (C) 2001 Academic Press.